1. Field of the Invention
The present invention refers to a roll bar of the kind provided on topless road vehicles for protecting vehicle occupants.
2. Description of Related Art
Roll bars for protecting vehicle occupants in the case of a roll-over accident are known not only in the field of motor racing but also for topless road vehicles or convertibles (cabriolet or roadster). The roll bar can be associated with only one vehicle occupant or, bridge the width of the vehicle, to protect two occupants sitting side by side. The roll bar is either fixedly installed or it is abruptly raised into position and locked in place in a critical driving situation. Known roll bars consist of a U-shaped hollow tube made of steel or light metal and having fastening points formed thereon. Load limits up to which the roll bar has to resist are predetermined by motor vehicle manufacturers for specific and typical cases of load and load directions. The main types of loads are a pressure-load acting on an apex region from above and a bending-load acting transversely to a plane defined by the roll bar. Fracture resisting requirements for the bending-load is normally less than half the fracture resisting requirements for the pressure-load. When the known roll bars, consisting of a metal tube, fulfill the bending-load requirements, they are unnecessarily oversized, approximately by a factor of two for the pressure-load requirements. Furthermore, the known tubular roll bars are heavy. The high weight requires a stable fastening to the vehicle body or, in the case of a retractable roll bar, a powerful retraction driving mechanism. In cases where the cross-section of the tube is opened by abrasion, due to the fact that the vehicle slides on the roll bar, the load requirements are no longer fulfilled.